1. Field of the Invention
This invention is related to a carbon heater, and particularly to a carbon heater suitable for use with a semiconductor manufacturing apparatus.
2. Description of the Prior Art
In the manufacturing process of semiconductors, for example, various heat treatments for a silicon wafer are carried out. In the manufacturing process of semiconductors accompanied by some kind of heating as described above, strict temperature control is required. Furthermore, it is important to keep the atmosphere of heating treatment clean.
For these reasons, it is earnestly desired that a high performance heater for a semiconductor manufacturing apparatus, which is excellent in heat-equalizing properties and temperature rising and decreasing properties, and which does not release contaminated substances, is developed and formed into products.
Japanese Patent Application Laid-Open No. 7-161725 Publication discloses, in a wafer heating apparatus, an electrode construction in which a graphite carbon fiber composite (hereinafter referred to as C/C) solidified and integrated using resins, is used for a heater.
Furthermore, in the aforementioned apparatus, a flat plate-like volute type SiC heater member or a complex-shaped Mo--Si heater member, subjected to welding process has been heretofore used.
In the aforementioned C/C heater member, if the member has a shape in which it is sufficiently large in two dimensions, it has an extremely high mechanical strength, even if it is thin in the third dimension. However, if the member has a longitudinally long shape having a one-dimensional length, i.e.,a width of less than 5 mm, a sufficient mechanical strength cannot be obtained in a case where the member is used as a heater for semiconductor manufacturing apparatus. In such a case when both ends of the member lengthwise are fixed to the terminals, a thermal load occurs with the thermal expansion of C/C, particularly in the vicinity of the terminal fixing portion, so that the member is easily broken.
Then on the other hand, if the width of the member is widened, the resistance value of the member decreases, which in turn requires a considerable increase in the electric current value in order to achieve the same level of heat generation. In addition, if the width of the member is widened, its thermal capacity increases, rendering rapid heating difficult.
Furthermore, when an attempt is made to obtain a complex-shape such as a nearly volute shape as shown in FIG. 3 of the aforementioned Japanese Patent Application Laid-Open No. 7-161725 Publication, slit processing for obtaining a heat-equalizing construction is difficult, and for obtaining the high resistance as mentioned above, it is necessary to narrow the width of the member. However, at present, such a processing is difficult and expensive and when processing commensurate with the costs is carried out, the heat-equalizing properties is never satisfactory.
Furthermore, in the above-described SiC heater member or Mo--Si heater member, an electric load density required for suppressing deterioration resulting from sublimation is merely approximately 20 W/cm.sup.2 and as a result, there was a limit in shortening of temperature rising speed. Also in these heater members, a sufficient heat resistance strength was not obtained in the complex-shape requiring a bend portion.
In the past, as a heater for a semiconductor heat treatment apparatus, a metal heater has been used sometimes. However, the metal heater had a problem in that metallic contamination was liable to occur, and the quality was liable to be unstable.
For enhancing the heat treatment efficiency of semiconductors, a heater capable of being rapidly raised and decreased in temperature is necessary. However, since the metal heater is high in thermal capacity, there was a limit in the improvement of these properties.
Further, since the metal heater is generally high in thermal capacity of supplementary equipment such as heat insulating materials, there was an inconvenience that the rapid temperature rising and decreasing were difficult.
Then, a carbon material, which is small in thermal capacity and excellent in high-temperature resistance in a non-oxidizing atmosphere has been utilized.
However, the carbon material using a normal electrode material or the like has a problem in terms of flexibility, causing a bottleneck to designing of its shape.
Furthermore, generally, in a carbon heater using a carbon wire as a heat generating element, a carbon wire is generally arranged within a container kept in a non-oxidizing atmosphere for prevention of oxidation. Since the carbon wire becomes very high in temperature when heat is generated, a bundle of a plurality of carbon wires is used as a terminal wire.
In the past, the carbon wire has been locked by impregnation and baking using a carbon paste. In the case of a relatively small-diameter carbon wire, it was sometimes locked by screwing.
However, in the locking method using the carbon paste, the carbon paste baked element sometimes becomes peeled off leading to an occurrence of dust.
On the other hand, in the screwing type locking method, in the case where the carbon wire bundle has many wires, the screwing work was cumbersome. Further, in the case of a large-diameter carbon wire, it could not sometimes be locked firmly.
In the heater using carbon wires as a heat generating element, a terminal device is also necessary to connect a terminal wire comprising a bundle of carbon wires to a metal terminal wire.
However, a terminal device capable of positively and easily connecting both the terminal wires has not yet been proposed.
Furthermore, in general, for keeping the atmosphere in the periphery of the carbon heat generating element a non-oxidizing atmosphere, the sealing technique of the carbon heat generating element is important.
However, in the conventional sealing system in which a carbon heat generating element is sandwiches between two quartz glass plates, outer periphery of which is welded, a strain or deformation occurs due to local heating, and stress is concentrated on the welded locking portion so that there is the great possibility of breaking the quartz.